One of the most important subjects in an Exchange design is the correct sizing ofthe enviroment. Microsoft has defined several guidelines which need to be used which are described on TechNet. Since today the Server Role Requirements Calculator has been added.
The first thing which had changed is the name, no it is not incorrect, you can also size the CAS role with it. In Exchange 2010 the Mailbox Role calculator was available to size your Mailbox server. But the new tool can be used to size both your CAS and Mailbox servers.
One remark must be made the tool can only be used to size an Exchange 2013 environment. For Exchange 2010 you will need to continue to use the Mailbox calculator.
If you would like to use the new calculator you can download it via the link below: